HIGH-FIELD TRANSPORT AND ELECTROLUMINESCENCE IN ZNS PHOSPHOR LAYERS

A full-band Monte Carlo simulation of the high-field electron transpor t in the ZnS phosphor layer of an alternating-current thin-film electr oluminescent device is performed. The simulation includes a nonlocal e mpirical pseudopotential band structure for ZnS and the relevant scatt ering mechanisms for electrons in the first four conduction bands, inc luding band-to-band impact ionization and impact excitation of Mn2+ lu minescent centers. The steady-state electron energy distribution in th e ZnS layer is computed for phosphor fields from 1 to 2 MV/cm. The sim ulation reveals a substantial fraction of electrons with energies in e xcess of the Mn2+ impact excitation threshold. The computed impact exc itation yield for carriers transiting the phosphor layer exhibits an a pproximately linear increase with increasing phosphor field above thre shold. The onset of Mn2+ impact excitation coincides with the onset of band-to-band impact ionization of electron-hole pairs which prevents electron runaway at high electric fields. (C) 1998 American Institute of Physics.